Field of the Invention
The present invention relates to a method of stacking fiber substrates which are used for fiber-reinforced resin molding by a resin injection method, and to a fiber substrate group composed of stacked fiber substrates.
Description of the Related Art
Vacuum assisted resin transfer molding (VaRTM) in which a resin (matrix resin) is injected into a cavity depressurized by evacuation has been practiced as a cost-competitive technique of fiber-reinforced resin molding, and structural members of an aircraft molded by VaRTM have been put into practical use.
When VaRTM is performed, a resin diffusion medium in a mesh form which presents a lower flow resistance to the resin than a fiber substrate is disposed on the surface of the fiber substrate to enhance the impregnation property of the resin (Japanese Patent No. 5322920). The resin injected into the cavity passes through the resin diffusion medium and is diffused along the surface of the fiber substrate, and the fiber substrate is further impregnated with the resin in the thickness direction.
A unidirectional fiber substrate in which bundles of fibers are disposed in parallel with one another is used as the fiber substrate (Japanese Patent Laid-Open No. 2005-22396). A number of the fiber substrates equivalent to the thickness of a member to be molded are stacked.
It is necessary to impregnate each layer of fiber substrates in a stack, which is composed of the plurality of fiber substrates, with a resin so that the resin spreads throughout the entire stack. The resin passes through a border zone between one fiber bundle and another of the fiber substrate, and the succeeding layer of the fiber substrate is impregnated with the resin.
However, the impregnation property of the resin deteriorates when the fiber substrates with their fiber bundles oriented in the same direction are successively stacked.
As shown in FIG. 9, when fiber bundles 21 of one fiber substrate 20 are disposed respectively on and along border zones 21B between adjacent fiber bundles 21 of another fiber substrate 20, the flow of the resin from the one fiber substrate 20 toward the other fiber substrate 20 disposed below is interrupted. Thus, the stack is more likely to be left unimpregnated in some portions as the number of the fiber substrates successively stacked with their fiber bundles 21 oriented in the same direction increases.
Therefore, the present invention aims to sufficiently impregnate each of stacked fiber substrates with a resin.